Osimhen was an option for PSG even in the last season. I think Osimhen could have even better performance in the last season when he was in the better form but now PSG knows they can't expect to see a miracle from this player but he can have a good performance like two years ago and he can be out of the good form like last season. I think there can be better options for PSG than Osimhen and they should not be worried and run for finding a replacement for Mbappe because Osimhen and Mbappe are not at the same level at all.
Your comparison isn't sounding solid, I know I'm the last season, towards the end of the league osimhen's performance did dropped and that too has affected his price but on a second taught it's possible there were factors that led to that which if taken care of he would do better, at PSG those factors that led to his poor performance may not be there but PSG still isn't a fit for him, his career may not do so well in PSG.
At the moment PSG isn't prioritizing getting him into the squad and he is yet to even show any interest in PSG as an option for his move, there were rumors of an interest in him by PSG last season before the end of the season but the deal didn't pull through and even now it's not looking like one that they would want to revisit again. Away from PSg, in other teams if osimhen gets and opportunity he's still gat some good potential.
Last season, Osimhen didn't score a lot of goals in every game. Hey, the whole Napoli team was pretty sleepy. Even the best players can get down in that mood. Picture him at PSG now. Not just blending in, but being the big man up top, enjoying the tasty passes from the midfield wizards they had. The guy was born to score goals, and PSG could be his dream team
Even though PSG isn't begging him to join right now, the transfer window is a crazy roller ride. In one month, anything can happen. They could wake up and smell the coffee all of a sudden, especially if they want to make their attack stronger. Trust me, Osimhen could be scoring like crazy in Paris if he had the right team behind him. Don't give up on him yet